1. Field of the Invention
The present invention pertains to a portable storage and mixing apparatus for bulk material such as cement mixtures including a generally horizontally disposed rear discharge drum having an improved configuration of mixing and discharge fins and a closure valve for the drum discharge opening.
2. Background Art
In the art of bulk material mixing units, particularly wet concrete mixers, it is conventional to provide a rotary mixing drum having two flights of internal helical fins to assist in the mixing operation and to provide for discharging the mixed material from the drum. Conventional portable or transit type wet concrete mixers are also characterized by a rotary drum having an inclined axis of rotation and a somewhat upwardly inclined discharge opening. Conventional transit concrete mixers are further characterized by the lack of a closure member over the discharge opening since the mixer drum is disposed at an upwardly inclined angle and the drum is normally rotated in a direction during mixing which causes the helical mixing fins to urge the material away from the discharge opening.
However, there are a number of applications for various types of cement materials wherein it is desirable to transport a dry mixture of cement and aggregate for mixing with water or other liquids at the site of application of the concrete itself. For example, in the cementing of oil wells, it is desirable to be able to transport casing cements and the like to the well site in quantities which may be easily transported by conventional highway truck and which may be stored on board the truck at the well site until required for use. Such applications for cement, as well as certain other bulk materials, require a storage and mixing unit which is capable of relatively rapid discharge of a uniform flow stream of dry bulk material at the work site wherein the liquid is added to the dry mixture just prior to cementing the well or other use of the material in its final application.
Conventional transit mixers for wet concrete mixtures are not well suited for the mixing and discharge of quantities of dry bulk materials. For example, as previously indicated, wet concrete mixers are typically designed with only two flights of mixing fins which are sufficient to assure that relatively continuous mixing of the material occurs during transit and prior to application, said mixing being primarily to prevent hardening of the mixture before it is discharged at the work site. The design of the mixing fins does not particularly seek, as a major objective, uniform flow of material out of the mixer drum during the discharge operation since the mixture is complete, that is, the liquid is already added in the mixing drum itself and a uniform flow rate is not as critical as with mixers wherein the liquid is added to the flow stream being discharged from the mixer drum.
Another problem associated with bulk material storage and mixing apparatus pertains to the control of the flow of material being discharged from the storage and mixing drum at the work site. The preferred arrangement of a generally horizontal cylindrical mixing drum provided with improved mixing and discharge fins has dictated the requirement for an improved discharge flow control device which also serves as a closure member for the drum discharge opening.
Accordingly, the present invention is directed to improvements in bulk material storage and mixing units which fill a particular need in regard to equipment adapted to handle dry bulk materials such as cement and cement aggregate substances wherein the requirements and desiderata for such types of storage and mixing units have not been met by prior art apparatus.